The Nervous System Nervous tissues Nervous tissue A

The Nervous System Nervous tissues Nervous tissue

A. Functions 1. Senses changes within and outside the body

2. Analyzes, stores, makes decisions with regards to changes 3. Responds to the changes

B. Organization 1. CNS - brain and spinal cord 2. PNS - cranial and spinal nerves which connect the CNS to the body.

(a) sensory/afferent neurons - carry impulses IN from sensory receptors to the CNS (b) motor/ efferent neurons - carry impulses OUT from the CNS to the muscle and glands

3. The PNS is subdivided into the SNS (from sensory receptors skeletal muscles - voluntary) and the ANS ( from motor neurons to smooth muscle, cardiac and glands using visceral effectors - involuntary).

4. The ANS is divided into a sympathetic division (expends energy / fight or flight response) and parasympathetic division (conserves and stores energy). Organs are usually connected to both.

C. Histology 1. The NS has 2 types of cells: neurons (conduct impulses and specialized functions) and neuroglia (support and protect neurons).

2. Types of neuroglia are shown on page 208.

3. Neuron structure is shown on page 209.

4. Myelin is a substance that covers the outside of some neurons and is used to insulate and increase the speed of an impulse. It is formed by Schwann cells. Multiple sclerosis and Tay-Sachs disease involve destruction of the myelin sheath.

5. Neural tissue groupings a. Nerve fiber - an extension out from a neuron cell body b. Nerve - several myelinated nerve fibers c. Tract - a bundle of nerve fibers d. White matter – groups of myelinated axons e. Gray matter – neurons cell bodies and dendrites or unmyelinated axons.

D. Functions 1. Conduction of an electrical impulse a. A neuron's plasma membrane has many ion channels.

b. In a resting neuron, there is a (+) charge on the outside of the PM and a (-) inside. This is the resting membrane potential (RMP). It is caused by the sodium-potassium pump (SP pump). The SP pump actively transports Na out, K in. Inside, there also several large (+) proteins.

c. Excitability is the ability of neurons to respond to stimuli (anything that can change a RMP) d. Events- review simulation notes e. Polarized Depolarized Repolarized (+) outside (-) outside (+) outside (-) inside (+) inside (-) inside

f. All or none principle: if a threshold stimulus (one that is strong enough to change the RMP) is applied, the impulse will proceed at maximum strength. More stimulus will not make it go better. A subthreshold stimulus (one that is NOT strong enough to change the RMP) is incapable of starting an action potential.

g. Types of conduction 1. Continuous – unmyelinated / moves along the entire neuron 2. Saltatory - myelinated - node to node jump

h. Impulse speed is determined by temperature (hot=fast), fiber diameter (big=faster), and myelin (yes=faster)

E. Conduction across synapses (junction between cells) 1. From a neuron to a muscle fiber is a neuromuscular junction 2. From a neuron a gland is a neuroglandular junction

3. Pathway Presynaptic neuron → synaptic knob (has synaptic vesicles with the neurotransmitter) → synaptic cleft → postsynaptic neuron which receives signals from many presynaptic neurons. It becomes an integrator.

F. Regeneration 1. Neurons lose their ability to reproduce around 6 months of age. 2. Damaged neurons are lost

3. Some regeneration is possible if it is myelinated OR the cell body is undamaged OR if the neuron is part of the PNS.